With the development of the society, video surveillance systems become more and more widely applied to meet ever-increasing security needs. As high quality video data often requires a large amount of storage resource, video compression technology develops continuously to reduce storage costs. However, most conventional video compression standards are not formulated for surveillance-use scenarios, and conventional compression technologies still result in a relatively high amount of information redundancy when used in video surveillance scenarios which are usually motionless. Therefore, an encoding method for surveillance environments to obtain same image quality at lower bit rates is needed to lower video storage costs.
In video encoding systems, an encoder may make use of different encoding technologies to compress video data. For example, one commonly used technology is predictive encoding. FIG. 1 is an example diagram showing a predictive encoding method. In a video stream, I Frames can be independently encoded using a spatial predictive encoding method. P Frames can be encoded using a temporal predictive encoding method and may need to use other frames as references for encoding. A P Frame can be encoded using a single previously encoded frame as a reference, or can also be encoded using multiple previously encoded frames as references. The frame(s) used by the P Frame as a reference(s) is/are called reference frame(s). When a P Frame is encoded, appropriate selection of reference frame(s) can result in better encoding quality or a lower encoding bit rate. However, to reduce encoding complexity and lower internal storage costs, the conventional encoding methods generally only store one reference frame, so that in many scenarios, no suitable matching blocks can be found (e.g., when a new background is exposed after an object moves).
Usually, the compression efficiency for P Frames processed with the temporal predictive encoding method is far greater than that of I Frames processed with the spatial predictive encoding method. Therefore, to improve compression efficiency, P Frames may be preferred for encoding over I Frames. However, for video encoding, an I Frame is often encoded once in a while mostly for two reasons: fast response for random frame location during playback, and reduction/prevention of error accumulation and spread resulting from predictive quantization.
Conventional encoding methods often have disadvantages. For example, when the conventional methods are used for video surveillance systems which primarily deal with motionless scenes, a large amount of redundant background information is encoded for I Frame encoding.
Hence it is highly desirable to improve the techniques for video encoding and decoding, e.g., to improve compression efficiency of surveillance videos.